Method and system for multi-carrier packet communication with reduced overhead

ABSTRACT

A method and system for minimizing the control overhead in a multi-carrier wireless communication network that utilizes a time-frequency resource is disclosed. In some embodiments, one or more zones in the time-frequency resource are designated for particular applications, such as a zone dedicated for voice-over-IP (VoIP) applications. By grouping applications of a similar type together within a zone, a reduction in the number of bits necessary for mapping a packet stream to a portion of the time-frequency resource can be achieved. In some embodiments, modular coding schemes associated with the packet streams may be selected that further reduce the amount of necessary control information. In some embodiments, packets may be classified for transmission in accordance with application type, QoS parameters, and other properties. In some embodiments, improved control messages may be constructed to facilitate the control process and minimize associated overhead.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of, and incorporates by reference inits entirety, U.S. patent application Ser. No. 14/720,554, filed on May22, 2015, which is a continuation of U.S. patent application Ser. No.14/248,243, filed on Apr. 8, 2014, now U.S. Pat. No. 9,042,337, which isa continuation of U.S. patent application Ser. No. 13/115,055, filed onMay 24, 2011, now U.S. Pat. No. 8,693,430, which is a continuation ofU.S. patent application Ser. No. 11/908,257, filed on Jul. 14, 2008, nowU.S. Pat. No. 7,948,944, which is a national stage application ofPCT/US06/38149, filed Sep. 28, 2006, which claims the benefit of U.S.Provisional Patent Application No. 60/721,451, filed on Sep. 28, 2005.

This application is related to, and incorporates by reference in itsentirety, U.S. patent application Ser. No. 13/631,735, filed on Sep. 28,2012, now U.S. Pat. No. 8,634,376.

TECHNICAL FIELD

The disclosed technology relates, in general, to wireless communicationand, in particular, to multi-carrier packet communication networks.

BACKGROUND

Bandwidth efficiency is one of the most important system performancefactors for wireless communication systems. In packet based datacommunication, where the traffic has a bursty and irregular pattern,application payloads are typically of different sizes and with differentquality of service (QoS) requirements. In order to accommodate differentapplications, a wireless communication system should be able to providea high degree of flexibility. However, in order to support suchflexibility, additional overhead is usually required. For example, in awireless system based on the IEEE 802.16 standard (“WiMAX”), multiplepacket streams are established for each mobile station to supportdifferent applications. At the medium access control (MAC) layer, eachpacket stream is mapped into a wireless connection. The MAC schedulerallocates wireless airlink resources to these connections. Specialscheduling messages, DL-MAP and UL-MAP, are utilized to broadcast thescheduling decisions to the mobile stations.

In the MAP scheduling message defined by IEEE802.16, there issignificant control overhead. For example, each connection is identifiedby a 16 bits connection ID (CID). The CID is included in the MAP messageto identify the mobile station. The maximum number of connections that asystem can support is therefore 65,536. Each mobile station has at leasttwo management connections for control and management messages and avarious number of traffic connections for application data traffic. Asanother example, each connection includes the identification of anairlink resource that can correspond to any time/frequency region thatis allocated for communication. The resource allocation is identified inthe time domain scale with a start symbol offset (8 bits) and a symbollength (7 bits) and in the frequency domain scale with a start logicalsubchannel offset (6 bits) and a number of allocated subchannels (6bits). Due to the fact that different applications have differentresource requirements, the allocated resource region is irregular fromconnection to connection. As a still further example, the modulation andcoding scheme for each connection is identified by a 4-bit MCS code,identified as either a downlink interval usage code (DIUC) or an uplinkinterval usage code (UIUC). Another 2 bits are used to indicate thecoding repetition in addition to 3 bits for power control. Overall, theoverhead of a MAP message is 52 bits. For applications such asvoice-over-IP (VoIP), the payload of an 8 Kbps voice codec is 20 bytesin every 20 ms. The overhead of the MAP message alone can thereforeaccount for as much as 32.5% of the overall data communication, therebyresulting in a relatively low spectral efficiency. It would therefore bebeneficial to reduce the overhead in a multi-carrier packetcommunication system to improve the spectral efficiency of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the coverage of a wireless communication network thatis comprised of a plurality of cells.

FIG. 2 is a block diagram of a receiver and a transmitter, such as mightbe used in a multi-carrier wireless communication network.

FIG. 3 is a block diagram depicting a division of communication capacityin a physical media resource.

FIG. 4 is a graphical depiction of the relationship between a samplingfrequency, a channel bandwidth, and usable subcarriers in a channel.

FIG. 5 is a graphical depiction of the structure of a multi-carriersignal in the frequency domain.

FIG. 6 is a block diagram of a time-frequency resource utilized by awireless communication network.

FIG. 7 is a block diagram of a classifier for classifying receivedpackets by application, QoS, or other factor.

FIGS. 8A and 8B are block diagrams of representative control messageformats.

FIG. 9 is a block diagram of a special resource zone with unit sequencedefined in time-first order.

FIGS. 10A-10C are block diagrams illustrating the reallocated ofresources within a resource zone.

DETAILED DESCRIPTION

A system and method for minimizing the control overhead in amulti-carrier wireless communication network that utilizes atime-frequency resource is disclosed. In some embodiments, one or morezones in the time-frequency resource are designated for particularapplications, such as a zone dedicated for voice-over-IP (VoIP)applications. By grouping applications of a similar type together withina zone, a reduction in the number of bits necessary for mapping a packetstream to a portion of the time-frequency resource can be achieved. Insome embodiments, modular coding schemes associated with the packetstreams may be selected that further reduce the amount of necessarycontrol information.

In some embodiments, packets may be classified for transmission inaccordance with application type, QoS parameters, and other properties.An application connection-specific identifier (ACID) may also beassigned to a packet stream. Both measures reduce the overheadassociated with managing multiple application streams in a communicationnetwork.

In some embodiments, improved control messages may be constructed tofacilitate the control process and minimize associated overhead. Thecontrol messages may include information such as the packet destination,the modulation and coding method, and the airlink resource used. Controlmessages of the same application type or subtype, modulation and codingscheme, or other parameter may be grouped together for efficiency.

While the following discussion contemplates the application of thedisclosed technology to an Orthogonal Frequency Division Multiple Access(OFDMA) system, those skilled in the art will appreciate that thetechnology can be applied to other system formats such as Code DivisionMultiple Access (CDMA), Multi-Carrier Code Division Multiple Access(MC-CDMA), or others. Without loss of generality, OFDMA is thereforeonly used as an example to illustrate the present technology. Inaddition, the following discussion uses voice-over-IP as arepresentative application to which the disclosed technology can beapplied. The disclosed technology is equally applicable to otherapplications including, but not limited to, audio and video.

The following description provides specific details for a thoroughunderstanding of, and enabling description for, various embodiments ofthe technology. One skilled in the art will understand that thetechnology may be practiced without these details. In some instances,well-known structures and functions have not been shown or described indetail to avoid unnecessarily obscuring the description of theembodiments of the technology. It is intended that the terminology usedin the description presented below be interpreted in its broadestreasonable manner, even though it is being used in conjunction with adetailed description of certain embodiments of the technology. Althoughcertain terms may be emphasized below, any terminology intended to beinterpreted in any restricted manner will be overtly and specificallydefined as such in this Detailed Description section.

I. Wireless Communication Network

FIG. 1 is a representative diagram of a wireless communication network100 that services a geographic region. The geographic region is dividedinto a plurality of cells 105, and wireless coverage is provided in eachcell by a base station (BS) 110. One or more mobile devices (not shown)may be fixed or may roam within the geographic region covered by thenetwork. The mobile devices are used as an interface between users andthe network. Each base station is connected to the backbone of thenetwork, usually by a dedicated link. A base station serves as a focalpoint to transmit information to and receive information from the mobiledevices within the cell that it serves by radio signals. Note that if acell is divided into sectors, from a system engineering point of vieweach sector can be considered as a cell. In this context, the terms“cell” and “sector” are interchangeable.

In a wireless communication system with base stations and mobiledevices, the transmission from a base station to a mobile device iscalled a downlink (DL) and the transmission from a mobile device to abase station is called an uplink (UL). FIG. 2 is a block diagram of arepresentative transmitter 200 and receiver 205 that may be used in basestations and mobile devices to implement a wireless communication link.The transmitter comprises a channel encoding and modulation component210, which applies data bit randomization, forward error correction(FEC) encoding, interleaving, and modulation of an input data signal.The channel encoding and modulation component is coupled to a subchanneland symbol construction component 215, an inverse fast Fourier transform(IFFT) component 220, and a radio transmitter component 225. Thoseskilled in the art will appreciate that these components construct andtransmit a communication signal containing the data that is input to thetransmitter 200. Other forms of transmitter may, of course, be useddepending on the requirements of the communication network.

The receiver 205 comprises a reception component 230, a frame andsynchronization component 235, a fast Fourier transform component 240, afrequency, timing, and channel estimation component 245, a subchanneldemodulation component 250, and a channel decoding component 255. Thechannel decoding component de-interleaves, decodes, and derandomizes asignal that is received by the receiver. The receiver recovers data fromthe signal and outputs the data for use by the mobile device or basestation. Other forms of receiver may, of course, be used depending onthe requirements of the communication network.

FIG. 3 is a block diagram depicting the division of communicationcapacity in a physical media resource 300 (e.g., radio or cable) intofrequency and time domains. The frequency is divided into two or moresubchannels 305, represented in the diagram as subchannels 1, 2, . . .m. Time is divided into two or more time slots 310, represented in thediagram as time slots 1, 2, . . . n. The canonical division of theresource by both time and frequency provides a high degree offlexibility and fine granularity for resource sharing between multipleapplications or multiple users of the resource.

FIG. 4 is a block diagram representing the relationship between thebandwidth of a given channel and the number of usable subcarriers withinthat channel. A multi-carrier signal in the frequency domain is made upof subcarriers. In FIG. 4, the sampling frequency is represented by thevariable f_(s), the bandwidth of the channel is represented by thevariable B_(ch), and the effective bandwidth by the variable B_(eff)(where the effective bandwidth is a percentage of the channelbandwidth). The number of usable subcarriers within the channel isdefined by the following equation:

${\#{\_ usable}{\_ subcarriers}} = {\frac{B_{eff}}{f_{s}} \times N_{fft}}$Where N_(fft) is the length of the fast Fourier transform. Those skilledin the art will appreciate that for a given bandwidth of a spectral bandor channel (B_(ch)), the number of usable subcarriers is finite andlimited, and depends on the size of the FFT, the sampling frequency(f_(s)), and the effective bandwidth (B_(eff)) in accordance withequation 1.

FIG. 5 is a signal diagram depicting the various subcarriers andsubchannels that are contained within a given channel. There are threetypes of subcarriers: (1) data subcarriers, which carry informationdata; (2) pilot subcarriers, whose phases and amplitudes arepredetermined and made known to all receivers, and which are used forassisting system functions such as estimation of system parameters; and(3) silent subcarriers, which have no energy and are used for guardbands and as a DC carrier. The data subcarriers can be arranged intogroups called subchannels to support scalability and multiple-access.The subcarriers forming one subchannel may or may not be adjacent toeach other. Each mobile device may use some or all of the subchannels.

A multi-carrier signal in the time domain is generally made up of timeframes, time slots, and OFDM symbols. A frame consists of a number oftime slots, and each time slot is comprised of one or more OFDM symbols.The OFDM time domain waveform is generated by applying aninverse-fast-Fourier-transform (IFFT) to the OFDM symbols in thefrequency domain. A copy of the last portion of the time domainwaveform, known as the cyclic prefix (CP), is inserted in the beginningof the waveform itself to form an OFDM symbol.

In some embodiments, a mapper such as the subchannel and symbolconstruction component 215 in FIG. 2 is designed to map the logicalfrequency/subcarrier and OFDM symbol indices seen by upper layerfacilities, such as the MAC resource scheduler or the coding andmodulation modules, to the actual physical subcarrier and OFDM symbolindices. A contiguous time-frequency area before the mapping may beactually discontinuous after the mapping, and vice versa. On the otherhand, in a special case, the mapping may be a “null process”, whichmaintains the same time and frequency indices before and after themapping. The mapping process may change from time slot to time slot,from frame to frame, or from cell to cell. Without loss of generality,the terms “resource”, “airlink resource”, and “time-frequency resource”as used herein may refer to either the time-frequency resource beforesuch mapping or after such mapping.

II. Airlink Resource Zones

Various technologies are now described that may be utilized inconjunction with the wireless communication network 100 in order toreduce the amount of control overhead associated with the use of systemresources. By reducing the control overhead, greater spectral efficiencyis achieved allowing the system to, among other benefits, maximize theamount of simultaneously supported communications.

FIG. 6 is a map of a time-frequency resource 600 that is allocated foruse by the wireless communication network 100. As described above, in atypical wireless system based on the IEEE 802.16 standard (“WiMAX”),multiple packet streams are established for each mobile device tosupport different applications. At the medium access control (MAC)layer, each packet stream is mapped into a wireless connection. As aresult, various applications carried in packet streams may be spreadthroughout the available time-frequency resource. To overcome theinefficiencies associated with maintaining this mapping, FIG. 6 depictsan alternative way of managing multiple packet streams. Thetime-frequency resource 600 may be divided into one or more zones 605 a,605 b, . . . 605 n. Each of the zones 605 a, 605 b, . . . 605 n isassociated with a particular type of application. For example, zone 605a may be associated with voice applications (e.g., VoIP), zone 605 b maybe associated with video applications, and so on. As will be describedin additional detail below, by grouping like applications together theamount of control overhead in MAC headers is reduced. Zones may bedynamically allocated, modified, or terminated by the system.

When applications of a similar type are grouped together within a zone,a reduction in the number of bits necessary for mapping a packet streamto a time-frequency segment can be achieved. In some embodiments, theidentification of the time-frequency segment associated with aparticular packet stream can be indicated by the starting time-frequencycoordinate and the ending time-frequency coordinate relative to thestarting point of the zone. The granularity in the time coordinates canbe one or multiple OFDM symbols, and that in the frequency coordinatescan be one or multiple subcarriers. If the time-frequency resource isdivided into two or more zones, the amount of control informationnecessary to map to a location relative to the starting point of thezone may be significantly less than the amount of information necessaryto map to an arbitrary starting and ending coordinate in the entiretime-frequency resource.

Within each zone 605 a, 605 b, . . . 605 n, the time-frequency resourcemay be further divided in accordance with certain rules to accommodatemultiple packet streams V₁, V₂, . . . V_(m). For example, as depicted inFIG. 6, zone 605 a is divided into multiple columns and the packetstreams are arranged from top down in each column and from left to rightacross the columns. The width of each column can be a certain number ofsubcarriers. Each packet stream V₁, V₂, . . . V_(m) may be associatedwith an application. For example, V₁ is the resource segment to be usedfor the first voice packet stream, V₂ is the resource segment to be usedfor the second voice packet stream, etc. While the zone 605 a is dividedand the packet streams numbered starting at an origin of the zone, itwill be appreciated that the division of the time-frequency resource inaccordance with certain rules may start at other origin locations withinthe zone as well. Segments within each zone may be dynamically allocatedby the system as requested and released by the system when expressly orautomatically terminated.

When the zones are further subdivided into time-frequency segments inaccordance with certain rules, a mapping of packet streams to segmentmay be achieved using a one-dimensional offset with respect to theorigin of the zone rather than the two-dimensional (i.e. startingtime-frequency coordinate and ending time-frequency coordinate relativeto the starting point of the zone) mapping method discussed above.Calculation of such an offset may require knowledge of a modulation andcoding scheme that is associated with a particular packet stream. Forexample, Table 1 below sets forth representative modulation andforward-error correction (FEC) coding schemes (MCS) that may be used forvoice packet streams under various channel conditions.

TABLE 1 Coding Raw MCSI Modulation rate Information bits symbols Units 116QAM ½ 160 80 1 2 QPSK ½ 160 160 2 3 QPSK ¼ 160 320 4 4 QPSK ⅛ 160 6408

In some embodiments, the MCS may be selected to utilize modularresources. For example, as illustrated in Table 1, 80 raw modulationsymbols are needed to transmit 160 information bits using 16QAMmodulation and rate-1/2 coding, the highest available MCS in the table.The resource utilized by this highest MCS is called a basic resourceunit (“Unit”), i.e., 80 raw symbols in this example. The resourceutilized by other MCS is simply an integer multiple of the basic unit.For example, four units are required to transmit the same number ofinformation bits using QPSK modulation with rate-1/4 coding. The MCSindex (MCSI) conveys the information about modulation and codingschemes. For a known vocoder, MCSI also implies the number of AMCresource units required for a voice packet. Those skilled in the artwill appreciate that coding and signal repetition can be combined toprovide lower coding rates. For example, rate-1/8 coding can be realizedby a concatenation of rate-1/2 coding and 4-time repetition.

The decision process for selecting the proper MCS of a packet can varyby application. In some embodiments, the process for voice packets canbe more conservative than that for general data packets due to the QoSrequirements of the voice applications. For example, when the signal tointerference noise ratio (SINR) is used as a threshold for selecting theMCS, the threshold value for voice packets is set higher than that forgeneral data packets. For example, the SINR threshold of QPSK withrate-1/2 coding for voice packets is 12 dB, while that for general datapackets is 10 dB.

If a MCS from Table 1 is selected for each packet stream contained in aparticular zone, the offset to a segment representing a particularpacket stream may be easily calculated. For example, an index VZI₁,VZI₂, . . . VZI_(m) is shown at the origin of each segment that iscontained in the zone 605 a. The index for any selected packet stream isdefined as the sum of all basic resource units associated with eachpacket stream preceding the selected packet stream, with an optionaladjustment depending on the location where the division of thetime-frequency resource is started (typically no adjustment is requiredsince the division starts at the origin of the zone). For example, thelocation index for the first voice packet stream is VZI₁=0 since itstarts at the origin of the zone 605 a. The first packet stream has anMCS of 1, which implies that one basic resource unit is used. As aresult, the index for the second voice packet stream is VZI₂=1. Thesecond packet stream has an MCS of 4, which implies that eight basicresource units are used. As a result, the index for the third voicepacket stream is VZI₃=9, arrived by summing the basic resource unitsused for the preceding first and second packet streams.

Using basic resource units as the granularity of a location offset tothe packet stream reduces the number of bits required to represent itslocation with the zone 605 a. For example, to support a maximum of 64VoIP calls in a cell, a maximum of 64×8=512 units might be used,assuming that every voice packet is transmitted using the lowest MCS.Therefore, a 9-bit number is sufficient to represent a VZI. In practice,different voice packets may be transmitted using different MCSs, somewith MCSI=1, some with MCSI=4, so on so forth. According to statistics,a shorter bit-length than the maximum needed, for example 8 bits, may beused for VZI for practical purpose.

In some embodiments, control information necessary to map a packetstream to a resource segment may be still further reduced. In the casewhere an MCS is used with packet streams that are located sequentiallyin the zone. The index of a packet can be inferred from the MCSI of thepackets located before the subject packet. For example, if the firstvoice packet stream uses MCSI₁=1, 16QAM with 1/2 coding, and the secondvoice packet stream uses MCSI₂=4, QPSK with 1/8 coding, then the firsttwo voice packet streams occupy 1+8=9 units, and the starting locationof the third voice packet stream is the 9th unit. Rather than encode theindex for each packet stream in the control information, the index canbe omitted in the control message and the offset from the origin of thezone calculated as necessary.

Allocation of the time-frequency resource 600 can be carried out in avariety of ways. In some embodiments, an application zone may containall subcarriers of one or multiple OFDM symbols or time slots. In someembodiments, the definition of an application zone, such as the locationand size of the zone, may be different from cell-to-cell 105. In someembodiments, in order to avoid inter-cell interference the zones ofsimilar applications are allocated at different locations in neighboringcells. For example, voice applications may be located at a lowerfrequency range in the time-frequency resource in one cell, and at ahigher frequency range in the time-frequency range in an adjacent cell.In some embodiments, the system allocates a fixed amount of resource toeach voice connection. The system uses AMC and matches it with adaptivemulti-rate (AMR) voice coding to improve the voice quality. Moreover,unused resources in one application zone may be allocated for otherapplications.

In a system with one or multiple application zones, the remainingresource unused by the application zones can be treated as a specialresource zone. The special resource zone may be irregular in shape. Forexample, FIG. 9 depicts a time-frequency resource 900 having threedefined zones 905, 910, and 915. The remaining resource area that isshaded in the figure represents the special resource zone. The MACscheduler may track the time-frequency resources in this special zoneand broadcast the resource allocation in a special zone MAP message. Insome embodiments, the special zone MAP message explicitly identifies theresource zone, for example using the time and frequency coordinates of aresource block. A mobile device can identify its own resource bydecoding the MAP message.

In some embodiments, both the base station and the mobile device sharethe configuration information of the special resource zone, and view thespecial zone as a contiguous resource zone. The MAP message onlyincludes the resource allocation information in the special resourcezone, using connection ID (described below), resource identificationparameters and MCS index.

In some embodiments, the MAP message can be further compressed if thespecial resource zone is further divided into a sequence of pre-definedresource units. For example, the shaded area in FIG. 9 has been furtherdivided into forty-two resource units 920, first numbered sequentiallyalong the time axis and then continuing in columns along the frequencyaxis. If the size of each resource unit is pre-defined, the locationwithin the special resource zone may be determined based on a mapping toa sequence number.

III. Application Connection IDs

When a mobile device enters a wireless network, it is first assigned abasic connection identification (BCID) for each direction of thewireless connection: downlink and uplink. A BCID can be used for controlmessages or generic (unclassified) application connections. The BCID fordownlink may or may not be the same as that of the uplink.

In some embodiments, a classification of packet streams may be performedby the system. FIG. 7 is a block diagram of a system component 700 forreceiving IP packets and sorting the received packets into variousstreams. The system component 700 includes a classifier 705 havingassociated classification rules 710. The classifier receives incomingpackets, each packet having various header information such as anEthernet header 715, an IP header 720, a UDP header 725, an RTP header730 and an RTP payload 735. The packets are classified by the classifier705 and output into different application data queues 740 where theywill subsequently be transmitted by an OFDMA transmitter 745.

The classifier 705 is able to classify the packets based on applicationtype, quality of service (QoS) requirement, or other properties. Forexample, packets from a voice application stream are identified based ona special value in the type of service (ToS) field in the IP header 720of the packets. A new combination of RTP/UDP/IP headers with the specialIP ToS field value indicates a new voice application stream. Such a newstream is identified by peeking into voice session setup protocolmessages, such as session initiation protocol (SIP). The classificationperformed by the classifier is based on one or more classification rules710. The classification rules can be configured statically ordynamically by a control process. Each classification rule is definedusing parameters, such as application type, QoS parameters, and otherproperties that may be determined from the received packets.

In some embodiments, the incoming packets may also be assigned anapplication connection-specific identifier (ACID) in addition to or inlieu of a BCID. Each ACID can be assigned to a corresponding packetstream. For example, an ACID can be assigned to voice packets thattogether make up a voice application. When an ACID is assigned to avoice application, the ACID may also be referred to as a voiceconnection ID (VCID). As another example, an ACID can be assigned to apacket stream that requires a particular QoS. Furthermore, anapplication packet stream can be further classified into differentsub-types, based on certain properties of that application. For example,voice applications can be further classified into different sub-typesbased on the voice source coding (vocoder) methods (e.g., G.711 andG.729A). When further classified in this matter, the sub-types may eachbe assigned their own ACID. For certain multi-casting applications, anACID may also be shared by multiple base stations or mobile devices.

Once established, the connection IDs, including BCIDs and ACIDs, aredisseminated, through broadcasting messages for example, to thecorresponding base station(s) and mobile device(s) for proper packettransmission and reception. As was previously discussed, the mediumaccess control (MAC) scheduler may allocate specific zones of airlinkresources for certain types of packet streams.

A connection ID is released once the wireless system determines thatthere is no need to continue the connection. For example, a voiceconnection and its VCID are released once the system detectsdeactivation of the voice stream. In some embodiments, the voiceconnection is deactivated if the voice session disconnect is detectedthrough snooping SIP signaling. In some embodiments, the voiceconnection is released if there is no voice packet activity on theconnection for a certain period of time.

In some embodiments, the same bit length is used in different types ofconnections IDs, including BCIDs and ACIDs. In some embodiments,different types of connection IDs may have different bit lengths. Forexample, in a typical implementation for voice applications, a BCID maybe 16-bits to accommodate a large number of mobile devices andunclassified applications, while a VCID is 6-bits to accommodate up to64 simultaneous voice connections in a cell. A shorter ACID length isbeneficial for reducing control overhead, especially when an applicationutilizes many small data packets, such as VoIP packets.

In some embodiments, an ACID is further augmented by other properties ofthe utilized airlink resources, such as time or frequency indices, toidentify an application connection. This can be used to further reduceACID bit length or to increase the maximum number of accommodatedapplication connections given a certain ACID bit length. For example, avoice codec generates voice application data periodically. Theallocation period is usually a multiple of the airlink frame duration.In this case, the airlink frame number can be combined with a VCID toidentify a voice connection. For example, the voice codec of G.723.1generates a voice frame once every 30 milliseconds. The MAC schedulerallocates airlink resource to such a voice connection once every 30 ms.In a wireless cellular system using 5 ms frame duration, a single VCIDcan be shared by 6 voice streams, each associated with a different framenumber to uniquely identify a voice connection.

IV. Control Messages

When airlink resource zones or application-specific IDs are utilized bythe system, various improved control messages, often called InformationElements (IEs), may be constructed to facilitate the control process andminimize the control overhead. Various control message improvements aredescribed herein.

In some embodiments, the IE is sent prior to transmitting an applicationpacket to indicate information associated with the packet, such as thepacket destination, the modulation and coding method, and the airlinkresource used. For example, the IE for a voice packet may include theVCID (indicative of the packet destination), the MCSI (encoding scheme),and the VZI (index to location fo the packet stream within the airlinkresource). In some embodiments, the VCID is 6 bits, the MCSI is 2 bits,and the VZI is 8 bits, thereby resulting in a 2-byte IE overhead foreach voice packet. Alternatively, the IE for a voice packet may includeonly the VCID and the MCSI, with the VZI inferred from the MCSIs ofprevious packet streams in the airlink resource as described above. Whenusing only the VCID and MCSI, the IE overhead for each voice packet isreduced to only 1 byte. Additional control information, such as powercontrol information, can be added to the IE with additional bit fields.The reduction in control bits improves the overall bandwidth efficiencyof the wireless communication network.

In some embodiments, a base station sends the IE before a downlinkpacket to inform the mobile device for proper reception of the packet,and the base station sends the IE before an uplink packet to inform themobile device for proper transmission of the packet. The downlink anduplink packet IEs may be separately grouped together. The IEs may bebroadcasted or multi-casted to corresponding destinations.

In some embodiments, the IEs of the same application type or subtype maybe grouped together. A special field, called an Application MAP (AMAP)subheader, for a specific application type, may be added to the IE. Thesubheader may indicate the application type and the length of the IEgroup. FIG. 8A is a block diagram of a representative IE 800 with anAMAP subheader 805, in this case used for voice applications. The AMAPsubheader 805 includes a type variable and a length variable. Asdepicted in FIG. 8A, type=01 indicates that the application type isvoice. Length=3 indicates that the subheader is followed by three voiceIEs. The remainder of the IE contains the three voice IEs 810 a, 810 b,and 810 c. For example, if the AMAP subheader was associated withstreams in the zone 605 a depicted in FIG. 6, then voice IE 810 a wouldpertain to packet stream V₁, voice IE 810 b would pertain to packetstream V₂, and voice IE 810 c would pertain to packet stream V₃. Thoseskilled in the art will appreciate that the although text is used toindicate the contents of the IE in FIG. 8A, in an actual implementationthe text would be replaced by appropriately coded information.

In some embodiments, the IEs for all packets that are transmitted withthe same modulation and coding schemes (MCS) are grouped together forefficiency. FIG. 8B is a block diagram of a block 850 of IEs that aregrouped by MCS. A frame control header (FCH) 855 or other controlmessage is transmitted prior to the block to indicate the length and theMCS used for each segment of the block. In some embodiments, adaptivemodulation and coding (AMC) is used for the transmission of the IE's. Aspecial rule, which is known to both base stations and mobile devices,can be used to determine the IE MCS, based on the MCS of itscorresponding packet for proper reception of the IE. In someembodiments, the MCS for an IE is maintained the same as that of itscorresponding application packet. In some embodiments, the MCS for an IEis one level more conservative than that of its corresponding packet.For example, if the MCSI for a packet is 2 (QPSK with rate-1/2 coding),then the MCSI for its IE is 3 (QPSK with rate-1/4 coding).

V. Voice Activity Detection

Typical voice conversations contain approximately 50 percent silence. Inorder to take advantage of the fact that about half of the time datadoes not need to be transmitted at the same rate as when a user isspeaking, the system may rely upon detecting the period of silence andreducing the effective data transfer rate during that period. Thesilence period in conversation is detected by a vocoder usingtechnologies such as Voice Activity Detection (VAD). Voice packets areonly generated when voice activity is detected. During the silenceperiod, the voice packet data rate is greatly reduced.

In addition to reducing the voice packet data rate during periods ofsilence, the bandwidth allocation for the voice connection may also bereduced. The MAC scheduler at the base station may use the indication ofvoice activity to adjust the bandwidth allocation for the voiceconnection. In the uplink direction, the mobile device sends a specialMAC message once a VAD indication is received from its vocoder. The MACmessage indicates to the base station that the voice data rate is beingtemporarily reduced. When such an indication is received, the MACscheduler can reduce the airlink resource allocated to the voiceconnection. Similarly, if the VAD indicates new voice activity, themobile device notifies the base station using a MAC message and theoriginal resource allocation is re-applied to the voice connection.

In the downlink direction, if there is no voice packet to be transmittedover a voice connection, the MAC scheduler allocates the resource toother voice connections. As a consequence, a resource block previousallocated for the connection in a particular zone may become vacant.Several methods can be used to deal with such fragmentation in the zone.

In some embodiments, the MAC scheduler at the base station reallocatesthe resource with the objective of minimizing the impact to other voiceconnections, such as their adaptive modulation and coding processes.

In some embodiments, the MAC scheduler maintains the resource allocationof the other voice connections, and allocates the resource vacated bythe silent voice connection to new voice connections or otherapplication packets.

In some embodiments, the MAC scheduler moves all the subsequentallocations up to fill the resource gap. As shown in FIG. 10A, once avoice connection, identified by VCID 2 enters a silent period, the othervoice connections are moved by the MAC scheduler to occupy the resourcevacated by VCID 2.

In some embodiments, the MAC scheduler uses the last voicetime-frequency resource in the same zone to fill the resource gap of asilent voice connection. FIG. 10B illustrates such a case, when the MACscheduler moves the last voice connection VCID 12 to occupy the resourceallocation gap that is vacated by the voice connection VCID 2.

In some embodiments, the MAC scheduler uses the last voicetime-frequency resource that has the same coding and modulation scheme,and is contained in the same zone, to fill the resource gap. Theresource gap that is introduced by such a replacement is then filled bythe voice time-frequency resource that is subsequent to the voicetime-frequency resource that was moved. As shown in FIG. 10C, voiceconnection VCID 6 uses the same coding and modulation scheme as voiceconnection VCID 2, and is the last connection having that scheme in thezone. When voice connection VCID 2 goes into a silent period, the MACscheduler allocates the voice connection VCID 2 resource to voiceconnection VCID 6. The MAC scheduler then moves resources after voiceconnection VCID 6, specifically VCID 7 in FIG. 10C, to occupy theresource allocation gap that is caused by moving voice connection VCID6.

The above detailed description of embodiments of the system is notintended to be exhaustive or to limit the system to the precise formdisclosed above. While specific embodiments of, and examples for, thesystem are described above for illustrative purposes, various equivalentmodifications are possible within the scope of the system, as thoseskilled in the relevant art will recognize. For example, while processesare presented in a given order, alternative embodiments may performroutines having steps in a different order, and some processes may bedeleted, moved, added, subdivided, combined, and/or modified to providealternative or subcombinations. Each of these processes may beimplemented in a variety of different ways. Further any specific numbersnoted herein are only examples: alternative implementations may employdiffering values or ranges.

These and other changes can be made to the invention in light of theabove Detailed Description. While the above description describescertain embodiments of the technology, and describes the best modecontemplated, no matter how detailed the above appears in text, theinvention can be practiced in many ways. Details of the system may varyconsiderably in its implementation details, while still beingencompassed by the technology disclosed herein. As noted above,particular terminology used when describing certain features or aspectsof the technology should not be taken to imply that the terminology isbeing redefined herein to be restricted to any specific characteristics,features, or aspects of the technology with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the invention to the specific embodimentsdisclosed in the specification, unless the above Detailed Descriptionsection explicitly defines such terms. Accordingly, the actual scope ofthe invention encompasses not only the disclosed embodiments, but alsoall equivalent ways of practicing or implementing the invention underthe claims.

We claim:
 1. An operating method for a wireless network comprising atleast a base station and a mobile station, the wireless networkemploying a frame structure of multiple frames for transmission, eachframe comprising a plurality of time intervals, each time intervalcomprising a plurality of orthogonal frequency division multiplexing(OFDM) symbols, and each OFDM symbol containing a plurality of frequencysubcarriers, the method comprising: assigning an identifier to themobile station; transmitting a signal containing information from thebase station to the mobile station over a segment of time-frequencyresource, the segment having a starting time-frequency coordinate andthe segment comprising N time-frequency resource units within a timeinterval, each unit containing a set of frequency subcarriers in a groupof OFDM symbols, where N=2, 4, or 8; and receiving by the mobile stationthe transmitted signal; and recovering by the mobile station theinformation from the received signal based on the startingtime-frequency coordinate and N in conjunction with the identifierassigned to the mobile station.
 2. The method of claim 1, wherein thestarting time-frequency coordinate indicates a starting OFDM symbol ofthe segment of time-frequency resource.
 3. The method of claim 1,wherein the starting time-frequency coordinate indicates a startingsubcarrier of the segment of time-frequency resource.
 4. The method ofclaim 1, wherein the starting time-frequency coordinate indicates astarting group of subcarriers of the segment of time-frequency resource.5. The method of claim 1, wherein modular coding is applied to thetime-frequency resource units in the segment of time-frequency resource.6. The method of claim 5, wherein a repetition coding is further appliedto the time-frequence resource units.
 7. A mobile device in a wirelesspacket system using a frame structure of multiple frames fortransmission, each frame comprising a plurality of time intervals, eachtime interval comprising a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols, and each OFDM symbol containing a pluralityof frequency subcarriers, the mobile device configured to: receive anidentifier from a base station in a cell in which the mobile device isoperating; and receive a signal containing information from the basestation over a segment of time-frequency resource, the segment having astarting time-frequency coordinate and the segment comprising Ntime-frequency resource units within a time interval, each unitcontaining a set of frequency subcarriers in a group of OFDM symbols,where N=2, 4, or 8; and recover the information from the received signalusing the starting time-frequency coordinate and N in conjunction withthe received identifier.
 8. The mobile device of claim 7, wherein thestarting time-frequency coordinate indicates a starting OFDM symbol ofthe segment of time-frequency resource.
 9. The mobile device of claim 7,wherein the starting time-frequency coordinate indicates a startingsubcarrier of the segment of time-frequency resource.
 10. The mobiledevice of claim 7, wherein the starting time-frequency coordinateindicates a starting group of subcarriers of the segment oftime-frequency resource.
 11. The mobile device of claim 7, whereinmodular coding is applied to the time-frequency resource units in thesegment of time-frequency resource.
 12. The mobile device of claim 11,wherein a repetition coding is further applied to the time-frequenceresource units.
 13. A base station in a wireless packet system using aframe structure of multiple frames for transmission, each framecomprising a plurality of time intervals, each time interval comprisinga plurality of orthogonal frequency division multiplexing (OFDM)symbols, and each OFDM symbol containing a plurality of frequencysubcarriers, the base station configured to: provide an identifier to amobile device in the cell; allocate a segment of time-frequency resourcefor carrying information to the mobile device, the segment having astarting time-frequency coordinate and the segment comprising Ntime-frequency resource units within a time interval, each unitcontaining a set of frequency subcarriers in a group of OFDM symbols,where N=2, 4, or 8; and transmit a signal containing the information tothe mobile device in a manner that allows the mobile device to recoverthe information using the starting time-frequency coordinate and N inconjunction with the provided identifier.
 14. The base station of claim13, wherein the starting time-frequency coordinate indicates a startingOFDM symbol of the segment of time-frequency resource.
 15. The basestation of claim 13, wherein the starting time-frequency coordinateindicates a starting subcarrier of the segment of time-frequencyresource.
 16. The base station of claim 13, wherein the startingtime-frequency coordinate indicates a starting group of subcarriers ofthe segment of time-frequency resource.
 17. The base station of claim13, wherein modular coding is applied to the time-frequency resourceunits in the segment of time-frequency resource.
 18. The base station ofclaim 17, wherein a repetition coding is further applied to thetime-frequence resource units.